This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. My research involves studying the structure and transport mechanism of the integral membrane transporter protein, GlpT, the glycerol-3-phosphate (G3P) transporter from E. coli. GlpT is a member of the major facilitator superfamily (MFS), the largest secondary membrane transporter family, with over 5000 known members. Prof. Wanga's lab previously determined the crystal structure of GlpT at 3.3 A resolution. Combining the structural information with biochemical data, we proposed a rocker-switch mechanism for substrate transport. I aim to understand GlpTs substrate specificity and substrate-induced conformational change by determining the crystal structure of GlpT in complex with a substrate. I have also grown crystals of wild-type GlpT that differ in habit from those used in previous studies. Cryo-cooling conditions are known for these crystals (which measure 100 um x 30 um x 30 um). It is hoped these crystals will diffract to a higher resolution and enable a better model of GlpT to be produced. If the diffraction data that derives from these crystals is good enough, the structure can be determined by molecular replacement.